Diclofenac or its salts possess excellent antiinflammatory action, and are widely used in clinics with oral and rectal dosage form. When administered orally or rectally, they are known to cause various side effects, including gastrointestinal tract disturbance. Because of this reason, a preparation for external application has been proposed, by which the drug is percutaneously absorbed without going through gastrointestinal tract and exhibits its action locally or systemically. However, since diclofenac and its salts are scarcely absorbed percutaneously, such a preparation has not been commercially sold.
Gel preparations, on the other hand, possess an advantage over other preparations for external application in terms of the good feeling upon use. When a gel preparation contains diclofenac or its salts as an active ingredient there are problems that a high concentration of diclofenac or its salts may destruct the gel structure, liquefying the gel or crystallizing over time.
In view of this situation the present inventors have undertaken extensive studies and found that if base components comprising a dibasic ester and a lower alcohol are gelatinized by using a nonionic polymer as a gelling agent, diclofenac or its salts can be contained at a high concentration and in a stable manner, providing gel preparations with excellent percutaneous absorptivity. The finding has led to the completion of the present invention.